It's an index of some of the stuff on the CPAN, broken down into categories,
sort of like the original Yahoo index. Or dmoz, which is
apparently still out there! Just like those indices, it's only a subset of the
total available content. Unlike those, things only appear on the module list
when the author requests it. Over the years, authors have become less and
less likely to register their modules, so the list became less relevant to
finding the best answer, which meant authors would be even less likely to
bother using it.

Some things that don't appear in the module list: DBIx::Class, Moose, Plack,
Dancer, Mojolicious, cpanminus, and plenty of other things you have heard of
and use.

Rather than keep the feature around, languishing, it's being shut off so that
we can, eventually, delete a bunch of code from PAUSE.